Process of treating metals with nitrogen



- No Drawing.

, gases tend to remain saturated.

Patented Apr. 28, 1931.

PATENT- OFFICE.

ROBERT J. ANDERSON, OF FAIBHONT,

FAO'I'URING COMPANY, OF FAIRMONT,

INIA.

My invention relates particularly to a process of treating molten alloys, etc., with nitrogen, and has relation especially to the treatment of the metals, particularly aluminum andits alloys, in this way to improve their physical characteristics. Molten metals, by which I mean to-include alloys, and especially aluminum and-its alloys, may, and usually do, contain dissolved and other impurities, such as foreign suspended matter. The dissolved gases presen therein depend upon the conditions under which the same is melted, the process of manufacture, etc., and, generally speaking, the gases present cannot be controlled efiecitively, or at all, under the conditionsof man ufacture. Where dissolved gases are present the eflect is to cause porosi' in the castings made therefrom, which is, 0 course, of eat moment in foundry practice as it lea s to rejection of castings, porosity, weakness, breakages, etc. It is found that metals dissolve increasing quantities of gases with increasing temperature of melting, thus dopartingfrom Henrys' law which applies to other liquids. Also, such metal-gas solutions That is to say, as the temperature is decreased from a high temperature the molten metal does not giveoflf gas at'the same rate at which the gas was taken up, and, on solidifying, there is a tendency for a considerable volume of gas to be evolved, causing blow-holes and porosity. I have discovered that these gases, and, also, other deleterious suspended solid impurities, by-which term I mean to include solids which become molten or not when thebody of metal is melted, may be removed by treatment of the metal with nitrogen, which is only dissolved with difliculty by the metal at 'a given temperature and which does not combine to an undesirable extent with the metal itself. I

The object of my invention is, therefore, to remove such gases and other deleterious matters from metals in the above manner. I

The theory of the action of .the removal thereof is not entirely known but it is believed that the action comprises mainly the metals, including WEST VIRGINIA, ABSIG NOB TO FAIR-KONG. mum- 'WEST A CORPORATION 01' WES! success or 'rqana'rme murals wrrn NITROGEN Application filed Ma 1, 1928. Serial in. 274,361.

removal of the dissolved gases and other deleterious impurities mechanically by agitation due to the introduction of the nitrogen as, as above referred to, although there may e, also, some combination brought about with the dissolved gases, or other deleterious impurities, as well. The deleterious solid impurities which are removed in this way are of various kinds, according to the particular kind of metal tgeated. These comprise, for example, sonims in steel, oxides in brass and bronze, dirt, nitride, carbide and oxide in aluminum, all of which have a deleterious effect on the mechanical characteristics of the metals. For instance,.in the case of steel, it has been found that dirty steel, containing some slag enclosures, is much inferior'in its properties to the steelfrom which these solid 1m uritieshave been removed. In fact, such inc usions have a harmful efiect on the fati e range, impactrresistance and other mec anical properties of the steel. Also, in

has very superior mes alumierties, as well as on the worki'gjgs, rolling and casting qualities of the met metal so treated is found to have greatly increased ,strength and'to be capzslleogffmucg n oun greater elongation. ,In fact, it previously substantially impossible to remove or reduce by' any previousl known method small percentages of impurities such as can be removed by my; rocess. I have found that even very sma percenta s of Also, the

impurities may be practically entire y removed by treatment in my process.

While-my invention is capable of embodiment in'many difierent forms, for the purpose of illustration I shall describeonly cer-' tain forms of my invention hereinafter.

For example, in carrying out my invention I find nitrogen to be very useful in the treatment of metals generally, such as those listed above, but it is especially applicable to the treatment of aluminum and its light alloys.

. For instance, in treating aluminum I provide a bath of molten aluminum which may have an desired temperature, such, for example, as 00 C. or above, and then apply the nitrogen gas to the metalas by bubbling it through the molten metal, thus causing agitation of the molten metal, until. the impurities are substantially entirely removed. This causes .flotation of the solid impurities due to the surface tension of the metal which sustains the impurities on the top of the body of metal. Thus, the introduction of say 1 cu. ft. of nitrogen, referred to standard conditions of temperature and pressure, per 300 lbs. of metal, may be ampleto remove dissolved gases and foreign suspended matter, after which the metal maybe poured to form a finished or semi-finished casting. In this from until the solid impurities are substantially entirely removed.

4. The process which comprises removing a solid impurity from a metal by the intermingl in of nitrogen therewith and the fiotation o the impurity due to the surface tension of the metal until the solid impurities are substantially entirely removed. 5. The process which comprises removing a solid impurity from aluminum by the intermingling ofnitrogen therewith and the flotation of the impurity due to the surface tension of the metal until the solid impurities are substantially entirely removed.

6. The process which comprises removing a solid impurity from a metal by the intermingling and combining of nitrogen therewith until the solid impurities are substantially entirely removed.

In testimony that I claim the foregoing I have hereunto set my hand this 28th-day of April, 1928.

ROBERT J. ANDERSON.

, treatment the gas may be applied to the metal in any desired way and in any desired type of apparatus, but, for example, the gas may be injected into the metalwith the aid of a perforated pipe, which may be located in the metal 'in such a way that the perforations therein for the discharge of the nitrogen are located at the bottom of the body of molten aluminum. The nitrogendoes not combine with the aluminum appreciably at the working temperature referred to but removes the dissolved gases and other deleterious impurities, some of which may have combined with the nitrogento some extent, but which are in any case effectively removed by the treatment. The dissolved gases pass ofi into the atmosphere while the solid inclusions join the top slag or dross and maybe removed by moved.

2; The process which comprises removing asohd impurity from aluminum by the interminglingof nitrogen therewith until the 1 solid impurities are substantially'entirely re-' moved.

' '3. The processwhich bomprises removing a solid impurity from a metal by. the intermingling of nitrogen therewith, thereby agitatmg the'm'etal tofree the impurities there- 

